The continued development, study, and analytical applications of novel anion/gas/polyion selective polymer membrane/film-based electrochemical and optical sensors are proposed. Research will build upon several exciting breakthroughs made during the most recent period of support focusing on new chemistries useful for fabricating anion and gas selective sensors using metalloporphyrins and similar metal-ligand complexes within thin polymeric films. Among these advances are the development of new optical and electrochemical sensors that display exceptional selectivity toward fluoride ion using Al(lll), Ga(lll) and Zr(IV)-complexes in low dielectric films. Future efforts will include both fundamental and applied studies and will concentrate on: 1) fully understanding the organic phase ligation chemistry of the various complexes that yield useful fluoride selective responses; 2) assessing whether hydroxide or fluoride ion bridged dimers of these species can form spontaneously within the polymeric films and whether this new dimer-monomer equilibrium reaction can be employed for opticalsensing of fluoride; 3) examining various strategies to prevent dimer-monomer equilibria from occurring within the polymer films and thereby prepare potentiometric membrane electrodes with Nernstian fluoride response, and 4) demonstrating practical applications of these new fluoride sensors for detecting fluoride in municipal drinking waters, and for use in conjunction with enzymes or metal ion catalysts to monitor toxic fluorophosphates (e.g., nerve gases). In addition, research will continue to assess whether metalloporphyrins and salophens not yet examined in detail (e.g., Co(lll), Mn(lll), Sn(IV), Tl(lll), Sc(lll), etc.) can undergo dimer-monomer chemistry within thin polymeric films. If so, efforts will be made to devise new and highly selective polymer film-based optical sensors for given anions (e.g., nitrite, salicylate, etc.), gases (including CO, NO, etc.) and other neutral species (e.g., alcohols, amines, etc.) based on the ability of such species to partition into the polymer films and break given metalloporphyrins dimers into monomers, yielding a large shift in the Xmax of the Soret band. It is anticipated that this research program will continue to provide the analytical community with a wide array of new and/or improved chemical sensors as well as novel sensor-based methods that will have immediate applications as tools for basic biomedical research and within modern clinical chemistry and environmental test instrumentation. In addition, given the potential high toxicity of fluoride ion in physiological systems, new and simple measurement tools for this species would be especially welcome.